A brushed DC motor conventionally comprises a rotor and a stator. The stator comprises a plurality of magnets, such as permanent magnets. The rotor comprises armature coil windings. In a brushed DC motor, brushes make a mechanical contact with a commutator to make an electrical connection between the armature coil windings of the rotor and a DC electrical source. As the rotor rotates, the stationary brushes come into contact with different sections of the rotating commutator. The different sections of the commutator are coupled to the armature coil in such a way that a current is switched to always flow through the armature coil closest to the stationary stator magnets.
In a brushless DC motor the magnets and the armature windings have switched places. Thus the rotor comprises a plurality of magnets, preferably permanent magnets, and the stator comprises the armature coils. This eliminates the problem of how to transfer current to a rotating armature. Brushless DC motors most commonly use an electronic controller instead of the brush commutator system. Brushless DC motors offer several advantages over brushed DC motors, including higher efficiency, higher reliability, reduced noise, and longer service life mainly due to elimination of brush erosion. Additionally ionizing sparks from the commutator are eliminated and there is an overall reduction of electromagnetic interference.
Since the windings are part of the stator instead of the rotor, they are not subjected to centrifugal forces. Additionally since the windings are located around the perimeter, they can be cooled by conduction to the motor casing requiring no airflow inside the casing for cooling. This in turn means that the motor can be entirely enclosed and protected from dirt or other foreign matter.
The downside of brushless DC motors is that they require somewhat complicated electronic controllers. The controller additionally requires some means of determining the rotor's orientation/position. Some designs use hall effect sensors or a rotary encoder, which might comprise hall effect sensors. The higher the power rating of the motor, the higher the accuracy of the rotor's orientation/position that is necessary to reduce losses and attain accurate control of the motor. Knowing the position/orientation of the rotor is important to attain optimal efficiency and be able to properly control torque, especially for low speeds and from standstill. There is still room for improvement on how to accurately determine the rotor orientation/position, especially of a brushless DC motor.